Process for producing a shaped graphite article



y 1963 J. WO'ODBURN, JR 3,089,195

PROCESS FOR PRODUCING A SHAPED GRAPHITE ARTICLE Filed Dec. 18, 1957INVEN TOR /ma {WW United States Patent 3,089,195 Patented May 14, 1963in the production of graphite molds and crucibles, as Well 3,089,195 asother graphite articles. PROCESS FOR PRO C A SHAPED Another feature ofthe invention is to fire an article James woodbmfmh giggg g gg g toArmed produced as above described without loss of contour and i Q l a oe Industries Incoi'porated, Chicago, Ill., a corporation of 5 gi supportof Shape dlstmguished from Pnor art New Jersey mg of pitch bondedmixtures which must be heated Filed 13, 1957 sex. No. 703,657 through aplastic stage before carbomzation occurs.

1 Claim. (Cl. 18-475) {\nother advantage of the invention is that acarbon article, formed as above described with a thermo-setting Thisinvention relates to the production of made-toresin, produces a moreuniform structure with respect to shape graphite articles, such as, forexample thermocouporosity because the binder does not liquify and mipletips, crucibles, and molds for high production castgrate during firingand because volatile pressure does ings. not distort the piece as in thecase of pitch bonded ar- According to prior art practices, graphitearticles have ticles. generally been produced by mixing carbonparticles, such 5 The foregoing and other objects and advantages of theas petroleum coke flour with pitch and then firing to invention willbecome apparent from a consideration of about 1500 F. to reduce thepitch to carbon. The arthe following specification and the accompanyingdrawticle is then slowly heated to about 5000 F. and held at ings,wherein: graphitizing temperature until the entire article is graph-FIGURE 1 is a microphotographic illustration at a itized. 20magnification of 5.5 showing graphitic structure produced A primarydisadvantage of such prior art techniques according to the novelprocess; and has been the necessity for supporting the article in shapeFIGURES 2-4 are similar microphotographic illustraas it is heatedthrough the plastic range of the pitch. tions at the same magnificationshowing graphitic struc- According to the invention, it has beendiscovered that ture produced according to prior art practices. amade-to-shape carbon article can be produced by mix- In general, thenovel process comprises the following ing carbon powder (known in theart as flour) at room basic steps: temperature with a thermo-settinghydro-carbon resin or binder such as furfuryl resin and a suitable acidcatalyst 2 2 2215 g gfgzg gi f g j gg 33 5;??? 5 preferably an organicacid such as maleic or phthalic anmofimmg hydnde' The mixture may beixtrudeci to shape or may (2) Shaping the mixture at room temperature bymoldbe pressed at room temperature into a die of steel or other in" orextrusion suitable material to form an article shaped to the con- (3)Curing the mixture to Set the binder. figuration of the die. The shapedarticle is then prefer- (4) Firing the mixture at a Sufiicienttemperature to ably removed from dle and as by heating i 35 duce thebinder to a carbon residue which bonds the an oven, to set the binder.Thereafter, the article 18 aggregate fired to carbonize the resin andthereby form an all (5) Impregnatron of the porous fired piece with ahy- Carbon amcle by heating {he .artlcle m Substannany dro-carbon suchas pitch where high strength is desired. oxygen-free atmosphere at asuitable temperature and at (6) Gm hmzin a suitable rate of temperatureincrease to carbonize the 40 p resin without cracking the article. Thefollowing Table No. lgives several examples of By means of this novelprocess, the time during which mixtures and curing procedures utilizedin the practice the mixture must be retained in the die is minimized,and of the invention:

Materials Parts Molding Curing Curing Article No. in Mix by ArticleProduced pressure (p.s.i.) Temp., Time,

Weight F. hr.

0 1 1}; 182 }Gear mold 1,000 20 b 100 2 3L 12g crucible,4 diameter, 5long 2,000 160 18 o 160 1,000 (bottom) 175 is 3 V 29 crucible, 8diameter, 10 long..."

1 2,000 (top) 230 1 4 1% 22 }valve mold 2,000 18 0 b0 5 ,1 53 .do.2,000.... 170 16 M .4 o 90 6 l 3 }Rocket Nozzle, 4 diameter 2,000 170 18Key: C-Petroleum coke-52% passes 200 Tyler Standard mesh-100% passes 100mesh;

Tsoot (such as is commercially sold under trademark Thermax); VFurfu'ry1resin;

MMaleic anhydride.

the cured articles may be conveniently stored, for a sulficient lengthof time to economically fire the articles in batches. Also, complicatedand difficult to machine surfaces may be formed on the articles withaccuracy and economy heretofore unknown in the art, as for example Ithas been discovered that the modulus of rupture of a graphite article,produced from a mixture such as above 70 described, is inadequate formost purposes if the binder content is less than 16 parts by weight; andexcessive squeeze-out of the binder occurs if the binder content exceeds24 parts by weight. This range of binder applies to articles and 6 onlywhere the mix consists of 10 parts of Thermax and 90 parts of coke.Mixes which contain 100 parts of coke and no 'Ihermax use more binderand can be-used in the range of 34 maximum and 24 minimum.

It has also been discovered that the molding pressure must be releasedand the article, if shaped in a die, should preferably be removedtherefrom before curing the article to set the binder. Otherwise, thereis a pronounced tendency for the article to crack or disintegrate duringfiring of the article to carbonize the binder.

In producing graphite articles according to the novel process it wasfound that an article cured in the mold within reasonable timelimitations is difiicult to fire without cracking or breaking. Thecuring time can be controlled by varying the acidity of the mix and thecuring temperature. To speed up the curing cycle, the acidity of the mixwas increased and the curing temperature was increased to about 350 F.;however when the article was contained in the mold during acceleratedcuring, water vapor given oif by the polymerization developed highpressures which stopped further polymerization. As a re suit, thearticle so formed literally exploded upon removal from the mold.

To eliminate the water vapor prior to molding, the mix was advanced forseveral hours at about 170 F., then molded and cured in the mold. Theprocess, under these conditions, was very difficult, to control; and thearticles so formed, as hereinafter discussed were difficult to firewithout cracking.

The articles listed in Table 1 were molded and then removed from themold. The articles were then cured as indicated in the table and weresubsequently fired to carbonize the binder.

In firing the articles, they were heated in a furnace to 1650 F. in anoxygen-free state. The pieces which had been cured in the mold weredifficult to fire, and temperature increases of as low as F. per hour inthe range of 3001000 F. caused cracking. Articles of the same size whichhad been cured after removal from the mold were successfully fired atrates of 100 F. per hour in the range of 3001000 F. The maximum firingrate for articles of this size formed by the prior art practice ofextruding pitch bonded mixtures is about 10 F. per hour.

After the articles had been fired, they were removed from the furnaceand several of the articles were impregnated with a solution consistingof equal parts of furfuryl alcohol and turfuraldehyde catalyzed with twopercent maleic anhydride. One of the articles was soaked in thissolution for fifty-four hours, then cured at 170 F. for 18 hours, andthen refired as above described. The weight gain of this article was5.9% indicating that somewhat less than half the pores were filled. Asecond article was subjected to a vacuum to remove air from the poresand was then covered with the solution using atmospheric pressure toforce the solution into the pores.

Weight gain of this second article after curing was 14.3%. The secondarticle was then refired at a rate of F. per hour and upon test provedto be sound.

The final step in the novel process consists of graphitizing thearticles, whether impregnated or not. This could be done by conventionalgraphitizing techniques in which the articles are packed in granularcoke covered with a silicon carbide layer at least eighteen inchesthick. According to prior art practices the articles are then resistanceheated in a furnace to a range of about 4600"- 5000 F.

According to the invention, the tired articles were placed in coveredcylindrical graphite containers within an induction coil. In someinstances, where the articles were large, single articles were placeddirectly within the coil. In packing the furnace, the container orsingle carbon article, as the case may be, was placed on three carbonpiers which rested directly on the furnace bottom. Carbon insulation inthe form of commercial soot known by the trade name Thermax was packedloosely under, around, and over the load. The coil was then energizedand balanced to unity power factor as per standard procedure in the useof such coils. The articles were graphitized without difiiculty and thecycle was much shorter than for comparable size articles graphitized ina conventional resistance furnace where the heat is generated in thegranular carbon between the pieces to be graphitized.

Graphite articles produced in accordance with the invention are equal inmechanical strength and have a higher electrical resistivity than priorart graphite articles. Furthermore, the graphitic structure poduced inaccordance with the novel process is superior to that produced by priorart methods.

FIGURES 1-4 are microphotographs showing the grain structure of graphiteproduced according to the invention and according to prior artpractices. FIGURE 1 is a magnification of 5.5 showing the grainstructure of the article identified as No. 5 in Table No. 1. It will beseen that the pores are much smaller and more evenly distributed thanthe commercial grades of graphite illustrated at a magnification of 5.5in FIGURES 2-4.

I claim:

In a method of producing a made-to-shape graphite article, the steps ofmixing carbon powder with a thermosetting furfuryl resin binder, thenshaping the mixture to form an article, then curing the article,unsupported as to its shape, to set the binder, then firing the article,unsupported as to its shape, to carbonize the binder, and thengraphitizing the article.

References Cited in the file of this patent UNITED STATES PATENTS1,556,990 Henry Oct. 13, 1925 1,804,052 Haas May 5, 1931 2,224,724 ElseyDec. 10, 1940 2,401,760 Heyroth June .11, 1946 2,761,848 Bushong et alSept. 4, 6

